Motion transmission system of a bicycle

ABSTRACT

A bicycle freewheel body and sprocket assembly is provided. The freewheel body has a predetermined axial width. The sprocket assembly has at least eleven sprockets of various diameters that are arranged on the freewheel body with a largest diameter sprocket and a smallest diameter sprocket forming end sprockets of the sprocket assembly. Each of the end sprockets has an outer face and the respective outer face of each end sprocket faces in an opposite directions and the outer faces are spaced from each other along the freewheel body predetermined axial width. An assembly of at least eleven sprockets has an overall axial width measured between respective outer faces of end sprockets in the assembly that is no greater than 40.5 mm. A chain is comprised of an alternating succession of inner and outer links, connected to each other at respective connection ends.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to: Italian patent applicationMI2007A001660, filed Aug. 9, 2007; U.S. application Ser. No. 12/187,560,filed Aug. 7, 2008, now issued U.S. Pat. No. 8,454,461; U.S. applicationSer. No. 13/279,834, filed October 24, 2011; U.S. application Ser. No.13/279,843, filed Oct. 24, 2011 (abandoned); and U.S. application Ser.No. 13/740,636, filed Jan. 14, 2013, all of which are incorporated byreference as if fully set forth.

FIELD OF INVENTION

The field of the invention relates to a motion transmission system of abicycle.

BACKGROUND

In a bicycle transmission system, the combination of a guide toothedwheel with a small diameter with a sprocket with a large diameter allowsdemanding climbs to be easily handled. However, this same combination,over flat land or going downhill, is disadvantageous since the cyclist'senergy is dissipated, due to the fact that the cyclist is obliged topedal quickly while the bicycle moves forwards slowly.

In order to make the aforementioned combination more suitable for theroute to be made, it is known to equip the bicycle with a plurality ofguide toothed wheels and with a plurality of sprockets, which can becombined with each other based upon requirements, through appropriategearshifting devices.

Because bicycle components have reached a high degree ofstandardization, the characteristic size of components such as frame,gearshifting devices, freewheel body or chain do not greatly vary, sothat most bicycles use three guide toothed wheels and up to tensprockets.

However, certain bicycle transmission systems show a sprocket assemblycomprising more sprockets, the largest of which are arranged partiallyover the spokes of the wheel of the bicycle. The sprockets have aminimum thickness, in the area of engagement with the chain, equal to1.76 mm, whereas the distance between adjacent sprockets is lower thanthe minimum thickness of the sprockets themselves, and in particular isequal to 1.66 mm. In order to be made to rotate, the sprocket assemblyillustrated requires the use of a special-shaped chain. Theaforementioned chain comprises, in alternating succession, a first link,consisting of two plates that are parallel and spaced apart to definethe area of engagement with a tooth of a sprocket, and a second link,consisting of a single plate shaped like a “bridge” so as to define in acentral portion thereof a seat for coupling with the next tooth of thesprocket.

The aforementioned chain, thanks to the second link made with a singleplate, has a maximum thickness much smaller than a conventional chainand for this reason it can also be used when there is a space betweenthe sprockets that is smaller than the thickness of the sprocketsthemselves.

The aforementioned chain wears down quickly because of the continuousfriction between the teeth of the sprockets and the second linksconsisting of a single shaped plate. This makes it subject to prematurestructural yielding.

Further, in such an arrangement, the sprockets that are arranged overthe spokes of the wheel have a large diameter, i.e. they have a veryhigh number of teeth. Since the number of teeth of the smallest sprocketof known sprocket assemblies is now standardized and goes up to about11-12 teeth, it follows that passing from the smallest sprockets to thelargest ones there is a non-linear increase in diameters, and thereforein the number of teeth. In other words, the cyclist notices a greatdifference in effort necessary to pedaling from one sprocket to anadjacent sprocket that has a great difference in teeth compared to theprevious one. Therefore, it is possible that the cyclist is not able tofind the optimum combination of sprockets and guide toothed wheels evenwith such a large number of sprockets.

In addition to the above, the total bulk of the sprocket assembly isvery high at the bicycle wheel, for which reason the chain, whenengaging the end sprockets, is inclined with respect to the guidetoothed wheels and therefore more subject to friction, wear and tensionpeaks.

SUMMARY

Throughout the present description and in the subsequent claims, theexpression “motion transmission system” in a bicycle is used to indicatethe assembly of at least some of the components active in thetransmission of motion, imparted by the cyclist through pedaling, fromthe crank arms to the rear wheel of the bicycle.

The present invention relates, in a first aspect thereof, to a motiontransmission system of a bicycle, comprising a sprocket assembly adaptedto be mounted on a freewheel body of a hub of a bicycle rear wheel and abicycle chain adapted to engage the sprockets of the sprocket assembly,the sprocket assembly comprising at least eleven sprockets, the hubbeing able to rotate about a rotation axis and comprising a plurality ofattachment seats of the spokes of the rear wheel of the bicycle and afastening portion to a frame of the bicycle, a predetermined axialdistance being defined on the hub between a plane, substantiallyperpendicular to the rotation axis, comprising the points of the spokeattachment seats closest to the freewheel body and a plane,substantially perpendicular to the rotation axis and defined in thefastening portion to the frame, comprising the attachment points to theframe closest to the freewheel body, wherein all of the sprockets of thesprocket assembly, when they are associated with the freewheel body,have an overall axial width or bulk smaller than, or equal to, thepredetermined axial distance, and in that the chain has a maximumthickness in the direction of the rotation axis comprised between 4.6 mmand 5.8 mm, the extreme values being included.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain characteristics and advantages shall become clearer from thefollowing detailed description of a preferred embodiment thereof, madewith reference to the attached drawings and given for indicating and notlimiting purposes. In such drawings:

FIG. 1 schematically shows a side view of a bicycle comprising a motiontransmission system;

FIG. 2 schematically shows a longitudinal section view of a portion ofthe motion transmission system of FIG. 1, i.e. of a sprocket assemblymounted on a freewheel body of a hub of a bicycle rear wheel, such asprocket assembly being engaged with a bicycle chain;

FIG. 3 schematically shows a plan view from above of the sprocketassembly of FIG. 2 mounted in a bicycle frame;

FIG. 4 schematically shows a plan view from above of a completetransmission system according to the present invention mounted on abicycle frame, FIG. 3 being an enlarged detail of this FIG. 4;

FIGS. 5 and 6 schematically show a plan view from above and,respectively, a top side view of the chain of FIG. 2;

FIG. 7 schematically shows a longitudinal section view of a portion ofthe chain of FIGS. 5 and 6, taken according to the plane traced with theline VII-VII of FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Introduction

The present invention relates, in a first aspect thereof, to a motiontransmission system of a bicycle, comprising a sprocket assembly adaptedto be mounted on a freewheel body of a hub of a bicycle rear wheel and abicycle chain adapted to engage the sprockets of the sprocket assembly,the sprocket assembly comprising at least eleven sprockets, the hubbeing able to rotate about a rotation axis and comprising a plurality ofattachment seats of the spokes of the rear wheel of the bicycle and afastening portion to a frame of the bicycle, a predetermined axialdistance being defined on the hub between a plane, substantiallyperpendicular to the rotation axis, comprising the points of the spokeattachment seats closest to the freewheel body and a plane,substantially perpendicular to the rotation axis and defined in thefastening portion to the frame, comprising the attachment points to theframe closest to the freewheel body, wherein all of the sprockets of thesprocket assembly, when they are associated with the freewheel body,have an overall axial bulk smaller than, or equal to, the predeterminedaxial distance, and in that the chain has a maximum thickness in thedirection of the rotation axis comprised between 4.6 mm and 5.8 mm, theextreme values being included.

The use of a sprocket assembly having the aforementioned axial bulk andof a chain having the aforementioned thickness allows, on the one hand,a high strength of the transmission system with at least elevensprockets to be ensured, at the same time allowing conventionally-shapedchain and sprockets to be used, to the advantage of the simplicity ofconstruction and reliability of the transmission system. In particular,the chain is smaller in size than the chains currently used for sprocketassemblies with ten sprockets, so as to allow narrower sprockets and/orsmaller distances between conventional sprockets to be used, whichresults in a lightweight assembly.

More specifically, although the maximum thickness of the chain is lessthan that currently used for a chain of a sprocket assembly with tensprockets, the aforementioned thickness of the chain ensures asurprisingly high strength, and in particular it is possible to use aconventionally-shaped chain, which is sufficiently strong, contrary tocertain prior art that suggests using a specially-shaped chain. Inaddition thereto, conventional chains, thanks to the presence of a bushable to rotate freely in the link engaged by a tooth, ensure that thefriction between the tooth and the chain does not limit the smoothrunning of the transmission system.

Moreover, the transmission system described herein provided for the useof a sprocket assembly in which no sprocket is intended to be arrangedover the spokes of the wheel of the bicycle, for which reason thesprockets added after the tenth one can advantageously be intermediatesprockets, and not end sprockets with a large diameter as required inthe prior art. This enormously increases the linearity of the increasein diameter of the sprockets, since it is possible for example to have agreater number of adjacent sprockets with a difference in teeth equal tojust one tooth.

Moreover, the use of a sprocket assembly having an axial bulk such as tobe able to be entirely housed on the freewheel body of the hub withoutbeing arranged over the spokes of the wheel allows such a sprocketassembly to be suitably positioned, for which reason it can be ensuredthat the chain, when engaging the end sprockets, is not excessivelyinclined, thus limiting its wear and the generation of tension peaks.

The chain may comprise an alternating succession of outer links andinner links, connected each other at respective connection ends, eachlink, outer and inner, comprising two respective plates, outer andinner, being arranged parallel and spaced apart to define a space forreceiving a tooth of a sprocket. The shape of the chain of thetransmission system may be conventional, which contributes to thesimplicity and cost-effectiveness of manufacturing the transmissionsystem.

The maximum thickness may be between 4.8 mm and 5.6 mm, the extremevalues being included. Preferably, the maximum thickness is comprisedbetween 5 mm and 5.5 mm, the extreme values being included. Theseaforementioned maximum thicknesses of the chain ensure a sufficientlyhigh reliability.

Preferably, the axial width or bulk is lower than or equal to 46 mm, andmore preferably lower than or equal to 43.5 mm.

In this way, the aforementioned sprocket assembly can be housed in aconventional bicycle having wheels and frame of standardized size.

The distance between two end sprockets of the sprocket assembly,measured between respective faces of the end sprockets facing outwardlyfrom the sprocket assembly, may be lower than or equal to 42.5 mm, andpreferably lower than or equal to 40.5 mm.

In this way the chain can engage the sprocket with the smallest diameterwith sufficient margin as not to slide in the frame of the bicycle, andthe gearshift can position the chain on the sprocket with the largestdiameter without interfering with the spokes of the wheel.

The sprockets may have a predetermined position and are spaced apart.

In another embodiment of the transmission system, the sprocket with thesmallest diameter of the sprocket assembly has 11 or 12 teeth and thesprocket with the largest diameter has a number of teeth comprisedbetween 23 and 27.

The transmission system has a sprocket assembly comprising a combinationof eleven sprockets selected from the following:

-   -   a first combination with sprockets having 11, 12, 13, 14, 15,        16, 17, 18, 19, 21, 23 teeth respectively;    -   a second combination with sprockets having 11, 12, 13, 14, 15,        16, 17, 19, 21, 23, 25 teeth respectively;    -   a third combination with sprockets having 11, 12, 13, 14, 15,        17, 19, 21, 23, 25, 27 teeth respectively;    -   a fourth combination with sprockets having 12, 13, 14, 15, 16,        17, 18, 19, 21, 23, 25 teeth respectively;    -   a fifth combination with sprockets having 12, 13, 14, 15, 16,        17, 19, 21, 23, 25, 27 teeth respectively.

In another alternative, the transmission system has a sprocket assemblycomprising a combination of twelve sprockets selected from thefollowing:

-   -   a first combination with sprockets having 11, 12, 13, 14, 15,        16, 17, 18, 19, 20, 21, 23 teeth respectively;    -   a second combination with sprockets having 11, 12, 13, 14, 15,        16, 17, 18, 19, 21, 23, 25 teeth respectively;    -   a third combination with sprockets having 11, 12, 13, 14, 15,        17, 18, 19, 21, 23, 25, 27 teeth respectively;    -   a fourth combination with sprockets having 12, 13, 14, 15, 16,        17, 18, 19, 20, 21, 23, 25 teeth respectively;    -   a fifth combination with sprockets having 12, 13, 14, 15, 16,        17, 18, 19, 21, 23, 25, 27 teeth respectively.

The sprockets may have a maximum thickness, at an engagement area withthe chain, lower than or equal to 1.7 mm, and more preferably lower thanor equal to 1.6 mm.

The distance between at least two consecutive sprockets of the sprocketassembly, measured between the engagement area with the chain of thesprocket with the smallest diameter and an adjacent sprocket, is greaterthan or equal to the thickness of the sprockets. Moreover, the distancebetween all of the consecutive sprockets of the sprocket assembly may begreater than or equal to the thickness of the sprockets.

The distance between consecutive sprockets may be lower than or equal to2.2 mm.

This makes it possible to use a chain with plates of the links havingrelatively large thicknesses and thus being sufficiently strong.

The sprockets with a smaller diameter may be placed at greater distancesapart than the sprockets with a larger diameter. Further, the sprocketswith a smaller diameter may be at a distance apart lower than or equalto 2.5 mm.

Such distances between sprockets allow the passage of aconventionally-shaped chain with particularly strong sections.

At least six consecutive sprockets may have a number of teeth thatdiffers by one from that of at least one adjacent sprocket. Moreover,one of the at least six sprockets has eighteen teeth.

Moreover, the consecutive sprockets may be at least seven in number.Even further, the consecutive sprockets may have at least eight or atleast nine in number.

In this way, in the movement of the chain from one sprocket to anotherthe cyclist does not notice a great difference in effort.

The transmission system may comprise at least one guide toothed wheelassociated with at least one crank arm and adapted to be engaged by thechain at the same time as one of the sprockets of the sprocket assembly.The at least one toothed wheel may be made from aluminum alloy and has amaximum thickness, in the engagement area of the chain, lower than orequal to 1.7 mm. Further, the maximum thickness of the at least onetoothed wheel and of the sprockets, in the respective engagement areasof the chain, is the same. In particular, the maximum thickness may belower than or equal to 1.6 mm in combination with a chain having athickness lower than or equal to 5.5 mm.

Thanks to the dimensions indicated above it is possible to make toothedwheels that are light and sufficiently strong.

In a second aspect thereof, the sprocket assembly for a bicycle rearwheel comprises at least eleven sprockets, wherein all of the sprocketsof the sprocket assembly have an overall axial width or bulk lower thanor equal to 46 mm.

Such a sprocket assembly may have, individually or in combination, allof the structural and functional characteristics discussed above withreference to the sprocket assembly of the motion transmission system andtherefore has all of the aforementioned advantages.

In particular, the axial bulk of the sprocket assembly is preferablylower than or equal to 43.5 mm.

The distance between two end sprockets of the sprocket assembly, may bemeasured between respective faces of the end sprockets facing outwardlyfrom the sprocket assembly, is lower than or equal to 42.5 mm, and morepreferably lower than or equal to 40.5 mm.

The sprockets may have a predetermined position and are spaced apart.

In another embodiment of the sprocket assembly, the sprocket with thesmallest diameter has 11 or 12 teeth and the sprocket with the largestdiameter has a number of teeth comprised between 23 and 27.

The aforementioned sprocket assembly may comprise a combination ofeleven sprockets selected from the following:

-   -   a first combination with sprockets having 11, 12, 13, 14, 15,        16, 17, 18, 19, 21, 23 teeth respectively;    -   a second combination with sprockets having 11, 12, 13, 14, 15,        16, 17, 19, 21, 23, 25 teeth respectively;    -   a third combination with sprockets having 11, 12, 13, 14, 15,        17, 19, 21, 23, 25, 27 teeth respectively;    -   a fourth combination with sprockets having 12, 13, 14, 15, 16,        17, 18, 19, 21, 23, 25 teeth respectively;    -   a fifth combination with sprockets having 12, 13, 14, 15, 16,        17, 19, 21, 23, 25, 27 teeth respectively.

In another alternative, the sprocket assembly may comprise a combinationof twelve sprockets selected from the following:

-   -   a first combination with sprockets having 11, 12, 13, 14, 15,        16, 17, 18, 19, 20, 21, 23 teeth respectively;    -   a second combination with sprockets having 11, 12, 13, 14, 15,        16, 17, 18, 19, 21, 23, 25 teeth respectively;    -   a third combination with sprockets having 11, 12, 13, 14, 15,        17, 18, 19, 21, 23, 25, 27 teeth respectively;    -   a fourth combination with sprockets having 12, 13, 14, 15, 16,        17, 18, 19, 20, 21, 23, 25 teeth respectively;    -   a fifth combination with sprockets having 12, 13, 14, 15, 16,        17, 18, 19, 21, 23, 25, 27 teeth respectively.

The sprockets may have a maximum thickness, at an engagement area with abicycle chain, lower than or equal to 1.7 mm, and more preferably lowerthan or equal to 1.6 mm.

The distance between at least two consecutive sprockets of the sprocketassembly, measured between the engagement area with a bicycle chain ofthe sprocket with the smallest diameter and an adjacent sprocket, may begreater than or equal to the thickness of the sprockets.

Moreover, the distance between all of the consecutive sprockets of thesprocket assembly may be greater than or equal to the thickness of thesprockets.

Preferably, the distance between consecutive sprockets is lower than orequal to 2.2 mm.

In another embodiment of the sprocket assembly, the sprockets with asmaller diameter may be placed at greater distances apart than thesprockets with a larger diameter. The sprockets with a smaller diametermay be at a distance apart lower than or equal to 2.5 mm.

At least six consecutive sprockets may have a number of teeth thatdiffers by one from that of at least one adjacent sprocket. Moreover,one of the at least six sprockets preferably has eighteen teeth.

Further, the consecutive sprockets may be at least seven in number. Evenfurther, the consecutive sprockets may be at least eight or at leastnine in number.

In a third aspect thereof, the bicycle chain comprises an alternatingsuccession of outer links and inner links, connected each other atrespective connection ends, each link, outer and inner, comprising tworespective plates, outer and inner, arranged parallel and spaced apartto define a space for receiving a tooth of a sprocket of a sprocketassembly of a bicycle rear wheel, wherein it has a maximum thicknesscomprised between 4.6 mm and 5.8 mm, the extreme values being included.

Such a bicycle chain has, individually or in combination, all of thestructural and functional characteristics discussed above with referenceto the chain of the motion transmission system and therefore has all ofthe aforementioned advantages.

In particular, the maximum thickness is between 4.8 mm and 5.6 mm, theextreme values being included, and more preferably between 5 mm and 5.5mm, the extreme values being included.

In a fourth aspect thereof, a bicycle comprises a transmission system,and/or a sprocket assembly and/or a chain of the type described above.

Such a bicycle may have, individually or in combination, all of thestructural and functional characteristics discussed above with referenceto the aforementioned transmission system and/or sprocket assemblyand/or chain.

In a fifth aspect thereof, a bicycle comprises a sprocket assemblyhaving at least eleven sprockets, wherein the sprocket assembly ispositioned so that the difference between the distance of the sprocketwith the smallest diameter from a chain line of the bicycle and thedistance of the sprocket with the largest diameter from the chain lineis lower than or equal, in absolute value, to 4 mm.

In such a bicycle, when the chain is in the engagement positions of theend sprockets, it is not excessively inclined and it is not subject towear and tension peaks.

The distance of the sprocket with the smallest diameter from the chainline is equal to the distance of the sprocket with the largest diameterfrom the chain line.

Description

With initial reference to FIG. 1, a bicycle 51 is shown to which amotion transmission system in accordance with the present invention isapplied, wholly indicated with 59.

The bicycle 51 of FIG. 1 comprises a frame 53 to which a front wheel 55and a rear driving wheel 57 are connected.

What makes the front wheel 55 different from the rear driving wheel 57is that the second receives the motion from the transmission system 59of the bicycle 51. This system comprises a pair of crank arms 50directly coupled with one or more guide toothed wheels 12. The crankarms 50 are supported in rotation in the frame 53 through a bottombracket assembly 14 comprising a shaft and some bearings. The guidetoothed wheels 12 engage a chain 15 to transmit the torque applied bythe cyclist on the crank arms 50 to a sprocket assembly 16 coupled withthe rear driving wheel 57.

In particular, the rear driving wheel 57 comprises a rim 58, some spokes18 and a hub 20. The hub 20 is per se known and for this reason is onlyschematically illustrated: it comprises a first body 56 (FIG. 3) coupledwith the rim 58 through the spokes 18 and a second body that rotates asa unit with the sprocket assembly 16. The second body is indicated withreference numeral 22 in FIG. 2 and is known as freewheel body since itis free to rotate with respect to the first body 56 in a direction ofrotation, and move it into rotation in the opposite direction. Therotation axis is indicated with X in FIG. 2.

On the first body 56 of the hub 20 there are seats 54 (FIG. 3) for theattachment of the spokes 18 to the hub 20. On the axially opposite sideto the seats 54, the hub 20 comprises a portion 540 for attachment tothe frame 53 of the bicycle 51.

The sprocket assembly 16 comprises a plurality of driven toothed wheels,known as sprockets, having a different outer diameter to one another: inthe example illustrated in FIGS. 2-4, there are eleven sprockets andthey are indicated with reference numerals 1 to 11, from the sprocket 1having the largest outer diameter to the sprocket 11 having the smallestouter diameter.

A gearshifting device 24, illustrated in FIG. 1, allows the chain 15 tobe moved from an engagement condition with a sprocket to an engagementcondition with another sprocket. A similar device can also be providedin the area of the crank arms 50 in the case in which there is more thanone guide toothed wheel 12. In this way the sprockets and the toothedwheels can be associated with each other through the chain 15 in aplurality of combinations.

With reference to FIGS. 2 and 3, the sprocket assembly 16 has a sizesuch as to be able to be entirely housed in the space of the hub 20between the portion 540 for attachment to the frame 53 of the bicycle 51and the portion of body 56 where the seats 54 are made. In particular,the sprocket assembly 16 is of a size such as to be able to be housed inthe space E between the planes Z and Y, where Z is the plane,perpendicular to the axis X of the hub 20, passing through the points ofthe seats 54 closest to the freewheel body 22, and Y is the plane,perpendicular to the axis X and defined in the portion for attachment tothe frame 53 of the hub, passing through the points of the hub 20 wherethe attachment to the frame 53 takes place and that are closest to thefreewheel body 22.

In particular, the portion of the frame 53 to which the wheel isfastened in general is shaped like a fork with a face facing towards thesprocket assembly 16, indicated with reference numeral 159 in FIGS. 2and 3 and the points of the hub 20 where the attachment to the frame 53takes place and that are closest to the freewheel body 22 are defined ata plane defined on the face 159.

The space E has a predetermined axial distance greater than or equal to46 mm and the sprocket assembly 16 has an axial bulk lower than or equalto 46 mm, preferably lower than or equal to 43.50 mm. Further, thesprocket with the smallest diameter 11 has a distance F from the face159 of the frame 53 at least equal to 2 mm or such that when the chain15 engages it the distance G of the chain 15 from the frame 53 is atleast equal to 0.5 mm.

Moreover, the distance M between the faces 1 a and 11 a of the sprockets1 and 11 facing towards the outside of the sprocket assembly 16 is lowerthan or equal to 42.5 mm, and preferably lower than or equal to 40.5 mm,compared with an engagement area of the sprockets made on the freewheelbody 22 with a length N lower than or equal to 39 mm.

With reference to FIG. 3 it can be seen that thanks to the size of thesprocket assembly 16 it can be positioned substantially symmetricallywith respect to the chain line LC of the bicycle 51, conventionallydefined by the standardization rules at a predetermined distance W fromthe middle plane MD of the bicycle 51 (in the case of use of a pair ofguide toothed wheels associated with the crank arms, the chain line isarranged substantially at half the distance between the two guidetoothed wheels). This means that the face 1 a of the sprocket 1 with thelargest diameter and the face 11 a of the sprocket 11 with the smallestdiameter have respective distances DS′ and DS″ from the chain line LCthat are substantially equal or with a difference lower than 4 mm.

This means that when the chain 15 is engaged respectively with thesprocket 1 with the largest diameter and with the sprocket 11 with thesmallest diameter it is inclined with respect to the chain line LC bysubstantially equal acute angles a′ and a″, as shown in FIG. 4.Preferably, the angles a′ and a″ are between 2.25° and 3.75°.

The sprocket assembly 16 meets the measurements indicated above sincethe sprockets from 1 to 11 have a thickness O substantially constantalong a radial direction, and lower than or equal to 1.7 mm and,moreover, the distance P between most of the adjacent sprockets isgreater than the thickness of the sprockets but lower than or equal to2.3 mm.

Actually, the thickness of the sprockets could also be variable along aradial direction, but what's more is that in the engagement area withthe chain 15 sprockets from 1 to 11 have a maximum thickness lower thanor equal to 1.7 mm and preferably lower than or equal to 1.6 mm.

Preferably, moreover, all of the sprockets are placed at a distance Papart lower than or equal to 2.2 mm.

Alternatively, some sprockets are at a distance apart greater than 2.2mm. According to the preferred embodiment shown in FIG. 2, the sprockets9, 10 and 11 are at distances apart P′ and P″ equal to 2.4 and 2.5 mm.

The chain 15 is illustrated in detail in FIGS. 5 to 7 and has aconventional shape. It comprises an alternating succession of outerlinks 60 and inner links 61, connected each other at respectiveconnection ends 60 a and 61 a.

Each outer link comprises two outer plates 15 a and each inner link 61comprises two inner plates 15 b. The plates of each link are arrangedparallel and spaced apart to define a space for receiving a tooth of asprocket. The outer plates 15 a are farther apart than the inner plates15 b and they partially overlap them at the respective connection end 60a and 61 a. A rivet 15 c rotatably joins the inner plates 15 b to theouter plates 15 a at the respective connection ends 60 a and 61 a.

In particular, the ends 60 a of the outer plates 60 have respectiveholes 60 b and the ends 61 a of the inner plates 61 have respectiveholes 61 b, the holes 60 b and 61 b having substantially the samediameter and being aligned to house the rivets 15 c. Around the rivet 15c, between the two inner plates 15 b, there is a bush 15 d capable ofrotating freely about the axis of the rivet (FIG. 7). Between the rivet15 c and the bush 15 d flanged portions 61 c of the inner plates 15 bare arranged, located around the holes 61 b and extending towards theinside of the link 61.

The maximum thickness R of the chain 15 is lower than or equal to 5.8 mmand preferably lower than or equal to 5.5 mm.

In any case, the chain has a minimum thickness greater than or equal to4.6 mm, preferably greater than or equal to 4.8 mm and even morepreferably greater than or equal to 5 mm. These values ensure sufficientstructural strength to satisfy the current technical standards. In thecase in which the guide toothed wheels 12 associated with the crank arms50 are made from aluminum alloy, at least in the part intended to engagethe chain 15, the latter preferably has a thickness comprised between 5and 5.7 mm.

With the sizes indicated above, some combinations of eleven sprocketsthat can be housed substantially in the space in which the combinationsof ten sprockets of the prior art are housed, are the following:

-   -   first combination with sprockets having 11, 12, 13, 14, 15, 16,        17, 18, 19, 21, 23 teeth respectively;    -   second combination with sprockets having 11, 12, 13, 14, 15, 16,        17, 19, 21, 23, 25 teeth respectively;    -   third combination with sprockets having 11, 12, 13, 14, 15, 17,        19, 21, 23, 25, 27 teeth respectively;    -   fourth combination with sprockets having 12, 13, 14, 15, 16, 17,        18, 19, 21, 23, 25 teeth respectively;    -   fifth combination with sprockets having 12, 13, 14, 15, 16, 17,        19, 21, 23, 25, 27 teeth respectively.

Some combinations with twelve sprockets are the following:

-   -   first combination with sprockets having 11, 12, 13, 14, 15, 16,        17, 18, 19, 20, 21, 23 teeth respectively;    -   second combination with sprockets having 11, 12, 13, 14, 15, 16,        17, 18, 19, 21, 23, 25 teeth respectively;    -   third combination with sprockets having 11, 12, 13, 14, 15, 17,        18, 19, 21, 23, 25, 27 teeth respectively;    -   fourth combination with sprockets having 12, 13, 14, 15, 16, 17,        18, 19, 20, 21, 23, 25 teeth respectively;    -   fifth combination with sprockets having 12, 13, 14, 15, 16, 17,        18, 19, 21, 23, 25, 27 teeth respectively.

Of course, a person of ordinary skill in the art can bring numerousmodifications and variants to the motion transmission system of abicycle described above, in order to satisfy contingent and specificrequirements, all of which are anyway covered by the scope of protectionas defined by the following claims.

What is claimed is:
 1. A bicycle freewheel body and sprocket assemblywherein: the freewheel body has a predetermined axial width, an outersurface that is configured to mate with one or more sprockets of thesprocket assembly, and an internal surface selected to mate with a hubassociated with a bicycle rear wheel; and, the sprocket assembly has atleast eleven sprockets of various diameters that are arranged on thefreewheel body with a largest diameter sprocket and a smallest diametersprocket forming end sprockets of the sprocket assembly, each of the endsprockets has an outer face and the respective outer face of each endsprocket faces in an opposite directions and the outer faces are spacedfrom each other along the freewheel body predetermined axial width; anassembly of at least eleven sprockets, that has an overall axial width,measured between respective outer faces of end sprockets in theassembly, that is no greater than 40.5 mm; and, a chain comprised of analternating succession of inner and outer links, connected to each otherat respective connection ends, each of the links comprising inner andouter plates that are arranged parallel to each other, the two plates ofboth the outer links and the inner links being spaced apart from eachother to define between the two plates a void space that receives atleast one tooth of at least one of the sprockets.
 2. The bicyclefreewheel body and sprocket assembly according to claim 1, wherein atleast one tooth of at least one sprocket has a maximum thickness that isno greater than 1.7 mm.
 3. The bicycle freewheel body and sprocketassembly according to claim 2, wherein the maximum thickness is nogreater than 1.6 mm.
 4. The bicycle freewheel body and sprocket assemblyaccording to claim 1, wherein the sprockets vary in size and a distancebetween teeth of least two consecutive sprockets of the assembly is atleast equal to an average thickness of the sprockets.
 5. The bicyclefreewheel body and sprocket assembly according to claim 4, wherein thedistance between the teeth sprockets of the assembly is at least equalto a thickness of any single sprocket.
 6. The bicycle freewheel body andsprocket assembly according to claim 4, wherein the distance between theteeth is no greater than 2.2 mm.
 7. The bicycle freewheel body andsprocket assembly according to claim 4, wherein sprockets with thesmallest diameter are arranged at greater distances apart than sprocketswith the largest diameter.
 8. The bicycle freewheel body and sprocketassembly according to claim 7, wherein the sprockets with the smallestdiameter are at a distance apart lower than or equal to 2.5 mm.
 9. Thebicycle freewheel body and sprocket assembly according to claim 1,wherein at least six consecutive sprockets have a number of teeth thatdiffers by one from that of at least one adjacent sprocket.
 10. Thebicycle freewheel body and sprocket assembly according to claim 9,wherein the consecutive sprockets are at least seven in number.
 11. Thebicycle freewheel body and sprocket assembly according to claim 10,wherein the consecutive sprockets are at least eight in number.
 12. Thebicycle freewheel body and sprocket assembly according to claim 11,wherein the consecutive sprockets are at least nine in number.
 13. Thebicycle freewheel body and sprocket assembly according to claim 9,wherein the at least six consecutive sprockets comprise a sprocket witheighteen teeth.
 14. Bicycle comprising a bicycle freewheel body andsprocket assembly according to claim
 1. 15. A motion transmission systemincluding a sprocket assembly of at least eleven sprockets defining asprocket assembly width between respective outer faces of end sprocketsof the sprocket assembly, wherein the sprocket assembly mounts to a hubthat rotates about a rotation axis and a predetermined axial distancebeing defined on the hub between a first plane, substantiallyperpendicular to the rotation axis, comprising at least one point ofattachment seats for spokes closest to a freewheel body of the hub, anda second plane, substantially perpendicular to the rotation axis anddefined at a frame attachment portion, wherein the sprocket assemblywidth is less than, or equal to, the predetermined axial distance,wherein a chain that engages the sprockets has a maximum thickness in adirection of the rotation axis between and including 4.6 mm and 5.8 mm,and wherein the chain comprises an alternating succession of outer andinner links, connected to each other at respective connection ends, eachof the links comprising two respective plates arranged parallel to eachother, the two plates of both the outer links and the inner links beingspaced apart from each other to define between the two plates a voidspace that receives a tooth of a sprocket, wherein the sprocket assemblywidth, measured between respective outer faces of end sprockets in theassembly, is no greater than 40.5 mm.
 16. A motion transmission systemincluding a sprocket assembly of at least eleven sprockets defining asprocket assembly width defined between respective outer faces of endsprockets of the sprocket assembly, wherein the sprocket assembly mountsto a hub that has a predetermined axial distance defined on the hubbetween a first plane, perpendicular to a rotation axis, comprising atleast one point of attachment seats for spokes closest to a freewheelbody of the hub, and a second plane, perpendicular to the rotation axisand defined at a frame attachment portion, wherein the sprocket assemblywidth is less than, or equal to, the predetermined axial distance,wherein a chain that engages the sprockets has a maximum thickness in adirection of the rotation axis between and including 4.6 mm and 5.8 mm,wherein the chain comprises an alternating succession of outer and innerlinks, connected to each other at respective connection ends, each ofthe links comprising two respective plates arranged parallel to eachother, the two plates of both the outer links and the inner links beingspaced apart from each other to define between the two plates a voidspace that receives a tooth of a sprocket, wherein the sprocket assemblywidth, measured between respective outer faces of end sprockets in theassembly, is no greater than 40.5 mm.
 17. A bicycle freewheel body andsprocket assembly wherein: the freewheel body has a predetermined axialwidth, an outer surface that is configured to mate with one or moresprockets of the sprocket assembly, and an internal surface selected tomate with a hub associated with a bicycle rear wheel; and, the sprocketassembly has at least eleven sprockets of various diameter that arearranged on the freewheel body with a largest diameter sprocket and asmallest diameter sprocket forming end sprockets of the sprocketassembly, each of the end sprockets has an outer face and the respectiveouter face of each end sprocket faces in an opposite directions and theouter faces are spaced from each other along the freewheel bodypredetermined axial width by a distance that is no greater than 42.5 mm;an assembly of at least eleven sprockets, that has an overall axialwidth, measured between respective outer faces of end sprockets in theassembly, that is no greater than 40.5 mm; and, a chain comprised of analternating succession of inner and outer links, connected to each otherat respective connection ends, each of the links comprising inner andouter plates that are arranged parallel to each other, the two plates ofboth the outer links and the inner links being spaced apart from eachother to define between the two plates a void space that receives atleast one tooth of at least one of the sprockets.
 18. A motiontransmission system comprising: at least eleven toothed sprockets in asprocket assembly that is mounted on a freewheel body having a frameattachment portion and a spoke attachment portion that are spaced apartby a predetermined axial distance; the at least eleven sprocketsassembly is mounted on the freewheel body with a largest diametersprocket and a smallest diameter sprocket being a respective endsprocket of the at least eleven sprockets assembly, wherein the largestdiameter sprocket is immediately adjacent to the spoke attachmentportion and the smallest diameter sprocket is immediately adjacent tothe frame attachment portion; and, a chain comprised of alternatinginner and outer links that are connected to each other, wherein, eachinner link and each outer link is comprising of two spaced apart platesthat define a void that receives one tooth of at least one of the atleast eleven toothed sprockets, and the chain remains within thepredetermined axial distance when it moves from the smallest sprocket tothe largest sprocket.